There are conventional arts as methods for melting cutting chips of nonferrous metal such as aluminum or magnesium by introducing them to molten metal and agitating the molten metal: (1) a method in which the cutting chips floating on the liquid surface of the molten metal are pushed with an implement such as a stick so as to soak them compulsorily to the molten metal; and (2) a method in which a propeller agitator is inserted into the molten metal through the liquid surface of the molten metal so as to agitate the molten metal.
However, in the methods (1) and (2), the implement and a propeller touch the molten metal with high temperature, whereby the implement and the propeller are worn. Therefore, it is necessary to exchange the implement and the propeller frequently, whereby the maintenance is troublesome.
In the methods (1) and (2), components of the broken implement or propeller may be mixed with the molten metal, thereby reducing the quality of the molten metal (the components may pollute the molten metal).
In addition to the above-mentioned methods, as a method in which cutting chips of aluminum are introduced to molten metal and the molten metal is agitated so as to melt the cutting chips, methods described in the Patent Literatures 1, 2 and 3 are known.
In the methods described in the Patent Literatures 1, 2 and 3, an inner space of a reverberatory furnace is partitioned into four chambers, a melting chamber, an open well part, a vortex generating chamber and a molten metal passage and these parts are communicated with each other so as to form a circulating passage of molten metal. An electromagnetic agitator constructed by an induction coil is arranged at the bottom of the molten metal passage and electromagnetic force is made act on the molten metal in the molten metal passage so as to circulate the molten metal in the molten metal passage, the melting chamber, the open well part, the vortex generating chamber, the molten metal passage, . . . in this order.
An opening (orifice) is formed at the bottom of the vortex generating chamber and the vortex generating chamber is communicated with the molten metal passage through this opening. When molten metal moving from the vortex generating chamber to the molten metal passage passes through the opening, a vortex is generated in the liquid surface of the molten metal in the vortex generating chamber. The aluminium metal cutting chips are rolled up by the vortex so as to melt the aluminium metal cutting chips.
However, in the methods described in the Patent Literatures 1, 2 and 3, the electromagnetic agitator generates electromagnetic force enough large for circulating the whole molten metal in the reverberatory furnace, whereby it is necessary to supply large electric power to the electromagnetic agitator.
Generally, when the aluminium metal cutting chips are introduced to the vortex generated in the liquid surface, the aluminium metal cutting chips float on the liquid surface of the molten metal and are not rolled up by the molten metal successfully, whereby the cutting chips are hardly melted.
Especially, the aluminium metal cutting chip has large surface area and the surface thereof is formed therein with an oxide layer having high melting point by temperature rise, whereby the aluminium metal cutting chip can hardly be melted. When the aluminium metal cutting chips float and retain in the liquid surface of the molten metal, the oxidization (combustion) of the aluminium metal cutting chips is advanced, in its turn yield of recycling by melting the aluminium metal cutting chips is reduced.
In the methods described in the Patent Literatures 1, 2 and 3, the molten metal moves to the molten metal passage passes through the opening formed in the bottom of the vortex generating chamber, whereby the aluminium metal cutting chips can finally be rolled up by the molten metal compulsorily. However, for generating strong vortex, it is necessary to make the sectional area of the opening of the bottom of the vortex generating chamber small to some degree. When a large quantity of the aluminium metal cutting chips are introduced to the molten metal at once, the unmelted aluminium metal cutting chips rush in the opening and clog the opening. Therefore, the processing speed (melting amount per unit time) of the aluminium metal cutting chips cannot be made very large.